This invention relates to air filters, which are enhanced by ionization. In particular it applies to pleated filters provided with means to produce ionization to increase trapping efficiency.
It is well known that charged particles are more readily captured by a filter medium than are neutral particles. In the prior art, one of the most common ionizing air filters is the Precipitator type. This is an electronic air filter in which ionizing wires of about 0.005 inches diameter, charged at about 7 Kilovolts, are placed between grounded plates to generate a corona and charge the dust particles passing therethrough. Further down the airflow path, alternating charged and grounded plates collect the charged particles of dust. The disadvantage of precipitator type filters is that they are difficult to maintain, requiring regular cleaning of the collector plates, which get loaded with fine dust. Cleaning often requires using very strong detergents. Another disadvantage of the precipitator type filter is that they produce a significant amount of ozone. This occurs because the charging wires are placed near grounded surfaces. This arrangement generates corona all along the length of the wires, which can be seen glowing in the dark.
In my U.S. Pat. No. 5,573,577, xe2x80x9cIonizing and Polarizing Electronic Air Filterxe2x80x9d, (Jun. 20, 2000) a method of producing ions in association with a trapping medium by electrifying conductive fibers is disclosed. Ions are generated at the exposed ends of string filaments which are made conductive by a carbon or graphite solution. This solution coats the strings, leaving the protruding, conductive fiber ends of the string exposed so that, upon application of high voltage, the fiber ends become sources of ions. Another aspect of my previous invention is that ions can be produced on the surface of a trapping medium by having xe2x80x9can ionizing grid 10 . . . formed by depositing conductive paint or colloidal graphite on a sheet of gauze 11. Gauze 11, because it is rendered conducting, functions the same way as fine wires 5 in effecting ionizationxe2x80x9d (see FIG. 5 in the above patent). The present invention is an improvement to my previous patents in combining ionizing elements with filter trapping medium.
Another U.S. patent is U.S. Pat. No. 4,715,870 (Dec. 29,1987) to Masuda, et al. This patent describes a Minipleat filter which is enhanced by attaching electrodes, in the form of conductive paint, to the folded edges of the Minipleat filter. A high voltage is then applied to these electrodes. In this patent, the applied voltage generates an electrostatic field which polarizes the media. This patent also discloses a series of ionizing wires and grounded plates much as in a precipitator located upstream from the filter in the airflow. These wires generate ions which charge particles of dust in the airflow to increase trapping efficiency in the pleated downstream pleated filter.
In the Masuda patent, there is no mention of any ionization taking place at the folded edges of the Minipleat filter. Unless the conductive paint used is such that it leaves pointed ends of the conductive fibers exposed, the use of conductive paint will not allow ionization to take place. In line 54 on page 3, the Masuda patent discloses that xe2x80x9ca leakage current rarely occursxe2x80x9d. If ions were being produced, then a current would be present. This suggests that the electrodes in this patent produce only polarization of the filter media and not ionization. Ionization requires current to occur between the electrodes.
An object of the present invention is therefore to provide a disposable, pleated filter that, through use of ionization, has a high efficiency. Another object of the invention is to provide a filter which has simple construction and is economical to operate.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
In a broad aspect the invention is directed to an air filtration system for placing in an air stream comprising:
1) a pleated, air permeable, filter medium of electrically insulative material having folded edges present both along an up-stream side and a down-stream side of said filter medium with respect to the direction of airflow to be passed therethrough,
2) exposed, conductive, pointed fiber ends located at least along the up-stream side of said filter medium,
3) a counter electrode in the form of ion-inducing conductive array positioned on the downstream side of the filter, and
4) a high voltage ionizing power supply connected through electrical coupling means at one side of its polarity to the conductive fiber ends, and connected at its other side to said conductive array, to thereby create an electric field between the conductive fiber ends and the conductive array that causes said conductive fiber ends to emit ions that will charge dust particles in an air stream and increase trapping efficiency.
More particularly, according to one variant, the invention employs a pleated filter comprising conductive strings having conductive fiber ends attached to the filter medium along the folded edges of the pleats of the filter. By applying high voltage to these strings, the fiber ends in the strings emit ions which charge the dust particles entering the filter, thus improving the efficiency of the filter.
According to another variation of the invention, a pleated filter of fibrous material is employed which itself provides fiber ends along the folded edges of the filter. Instead of having coated strings, the folded edges of the pleated filter medium may be coated with a conductive solution so that fiber ends within the coated, fibrous filter medium are left exposed and produce the ions when charged by the power supply. The downstream, folded edges of the pleated filter may be similarly coated to provide the ion-inducing conductive array.
By a further variant of the invention a conductive fibrous mesh having multiple pointed fiber ends contained therein is positioned along the upstream folded edges of the pleated filter medium. Electrification of the pointed fiber ends within the mesh produces ions which charge dust particles entering the pleated medium.
Because the pointed ionizing elements employed in this air filtration system, produce a very small amount of corona, the system requires only a small amount of current to operate. The test filter in question operated on a high voltage power supply that required only approximately three (3) watts of power from a 24V AC originating source to drive the power supply. Because of the low current demands placed on the high voltage power supply, it may have high internal impedance. This reduces the shock risk to users who may inadvertently touch high potential components.
The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.